Saturday, January 9, 2010

Fractional-reserve banking is the banking practice in which banks keep only a fraction of their deposits in reserve (as cash and other highly liquid assets) and lend out the remainder, while maintaining the simultaneous obligation to redeem all these deposits upon demand Fractional reserve banking necessarily occurs when banks lend out any fraction of the funds received from deposit accounts. This practice is universal in modern banking, and is to be contrasted with full-reserve banking which died out over two centuries ago.

By its nature, the practice of fractional reserve banking expands money supply (cash and demand deposits) beyond what it would otherwise be. Because of the prevalence of fractional reserve banking, the broad money supply of most countries is a multiple larger than the amount of base money created by the country's central bank. That multiple (called the money multiplier) is determined by the reserve requirement or other financial ratio requirements imposed by financial regulators, and by the excess reserves kept by commercial banks.

Central banks generally mandate reserve requirements that require banks to keep a minimum fraction of their demand deposits as cash reserves. This both limits the amount of money creation that occurs in the commercial banking system, and ensures that banks have enough ready cash to meet normal demand for withdrawals. Problems can arise, however, when a large number of depositors seek withdrawal of their deposits; this can cause a bank runor, when problems are extreme and widespread, a systemic crisis. To mitigate these problems, central banks (or other government institutions) generally regulate and oversee commercial banks, act as lender of last resort to commercial banks, and also insure the deposits of the commercial banks customers.